What describes the ability and willingness to buy a good or service at a given price?

The correct answer is demand, which refers to both the willingness and ability of consumers to purchase a good or service at a specific price. It illustrates a fundamental concept in economics, where demand is determined by various factors, such as consumers' preferences, their income, and the prices of related goods. When demand increases, it typically signifies that consumers are prepared to purchase more of a product at the same price or are willing to pay higher prices for the same quantity, indicating robust market activity.

In the context of supply, it is concerned primarily with the producers' side of the market, focusing on the quantity of goods that businesses are willing to sell at various prices. "Market" refers to the overall system where buyers and sellers interact, encompassing various dynamics, including price determination and the exchange of goods, but does not specifically define consumer behavior alone. Utility pertains to the satisfaction or benefit derived from consuming a good or service; while related, it does not describe purchasing behavior directly. Therefore, demand is the most accurate term for the ability and willingness to buy.